Sonnen has nothing to lose. He's smaller and just lost.
Jones has nothing to gain.
I can see where Jones would not want it. Plus, the fight will be there later and they will have more than 8 days to hype it. If Jones loses to Karate Man, they will do Jones/Sonnen with far more hype. If Jones wins and Sonnen gets a 205 win, they will do a title fight with far more hype.
People are mad at Jones, but this is on Zuffa and their terrible business model.